1. Field of the Invention
The invention relates to a bias circuit for use with a weighted current source of a digital-to-analog converter. In particular, the invention relates to a bias circuit supplied to a weighted current source component of the digital-to-analog converter, to provide a well-compensated gate voltage to the weighted current source, and thereby allow for precise conversion of an n-bit digital word to an analog signal.
2. Description of the Related Art
In designing and manufacturing digital-to-analog converters (D/A) as an application specific integrated circuit (ASIC), problems arise in that the electrical characteristics of the individual components making up the ASIC may vary with temperature and may not maintain the precise values that they are designed for. For example, parameters of a 1 kohm resistor used in an ASIC may vary as the temperature of the ASIC varies. Additionally, when manufacturing ASICs, individual components of the ASIC may vary from their specified values by 50% or more. Again, for example, a resistor may be designed to have a resistance of 1 kohm, but the ASIC manufacturing process may result in that resistor having an actual resistance of 1.5 kohm.
Given this uncertainty in component characteristics due to the manufacturing process of ASICs, as well as the fact that individual components in an ASIC have characteristics that vary with temperature, a problem exists in that even though the D/A ASIC is designed to operate properly and precisely, in actual practice it does not perform well due to the temperature variations and/or manufacturing inaccuracies introduced.
It is therefore desirable to have a D/A ASIC that accurately performs D/A conversion even with temperature variations, and that operates the same even with variations in the actual individual components of the D/A ASIC due to manufacturing inaccuracies of the individual ASIC components.